Methylomarinum vadi gen. nov., sp. nov., a methanotroph isolated from two distinct marine environments

Two aerobic methane-oxidizing bacterial strains were isolated from distinct marine environments in Japan. Strains IT-4^T and T2-1 were Gram-stain-negative, aerobic, motile, plump short rods or oval-shaped bacteria with a single polar flagellum and type I intracytoplasmic membranes. They were obligate methanotrophs that grew only on methane or methanol. Each strain possessed the particulate methane monooxygenase (pMMO). The ribulose monophosphate pathway was operative for carbon assimilation. The strains grew best at 37 °C, and did not grow at 45 °C. NaCl was required for growth within a concentration range of 1–8 % (w/v). The major phospholipid fatty acids were C_16 : 0, C_16 : 1ω7c, and C_16 : 1ω5t. The major isoprenoid quinone was MQ-8. The DNA G+C content was 50.9–51.7 mol%. The 16S rRNA gene sequences of the strains showed 99.4 % similarity to each other, and DNA–DNA hybridization analysis indicated that the strains were representatives of the same species. The 16S rRNA gene sequences were highly similar to some marine environmental sequences (94.0–97.7 % similarity), but did not show similarities more than 94 % with sequences of members of other related genera, such as Methylomicrobium, Methylobacter, Methylomonas and Methylosarcina. Phylogenies based on 16S rRNA gene sequences and deduced partial PmoA sequences, and the physiological and chemotaxonomic characteristics revealed that strains IT-4^T and T2-1 represent a novel species of a new genus in the family Methylococcaceae, for which the name Methylomarinum vadi gen. nov., sp. nov. is proposed. The type strain is IT-4^T ( = JCM 13665^T = DSM 18976^T).